Conventionally, an X-ray apparatus includes a grid for reducing image quality degradation due to scattered X-rays. However, when the grid is used, a fine longitudinal pattern due to grid foil shadows is superimposed on radiographic images.
An FPD (Flat Panel Detector) has been used widely as an X-ray detector in recent years. The FPD brings about improvements in the spatial resolution and X-ray sensitivity of radiographic images, and its use is increasing at a rapid rate. However, the greater improvements made in spatial resolution and X-ray sensitivity make the clearer grid foil shadows, which are obstructive to interpretation of radiographic images. In order to remove these grid foil shadows, Patent Document 1 discloses a removing method based on image processing using frequency conversion.
On the other hand, Patent Document 2 discloses a synchronous grid for an FPD. As shown in FIG. 23, a synchronous grid 43 includes grid foil strips 43a arranged as inclined such that each has flat surfaces aligned to a straight line 42 extending between a focus F of an X-ray source 41 and an X-ray detecting plane of an FPD 44. That is, the grid foil strips 43a are inclined to align with direct X-rays.
As shown in FIG. 24, the synchronous grid 43 has the grid foil strips 43a arranged so that grid foil shadows may fall on middles of detecting pixels 47 of the FPD 44. In this way, the positions of the grid foil strips 43a and detection pixels 47 are arranged synchronously. Since scattered X-rays 45 are absorbable by these grid foil strips 43a, noise due to the scattered X-rays 45 can be removed. As distinct from the conventional type grid, the synchronous grid 43 uses no spacers such as of graphite between the grid foil strips 43a. Therefore, direct X-rays 46 are not absorbed, whereby the efficiency of detecting the direct X-rays 46 can be increased.
The grid foil strips of the synchronous grid have the same grid ratio as the grid foil strips of the conventional asynchronous grid, although the intervals between the grid foil strips are different. The synchronous grid has intervals Gp between the grid foil strips, which are longer than those of the asynchronous grid. However, the height A of the grid foil strips along the direction of incidence of direct X-rays is higher in the synchronous grid than in the asynchronous grid. With such construction, grid ratio A/Gp of the synchronous grid can be set equal to the grid ratio of the asynchronous grid. Thus, even if the intervals between the grid foil strips Gp in the synchronous grid are longer than in the conventional grid, by making the height A of the grid foil strips higher, performance in removing noise due to the scattered X-rays 45 can be made the same.